Previously, counterbalancing has been used for placement of robotic surgical arms in a static position prior to surgery. However, conventional counterbalancing mechanisms suffer from a number of disadvantages.
For instance, previously, robotic surgical arms have been positioned using conventional counterbalancing mechanisms. One conventional counterbalancing mechanism involves a constant force spring (CFS) assembly that controls the winding and unwinding of a spring member having at most three (3) laminations, namely three layers of material placed substantially in parallel and substantially in close physical proximity to each other, which wind and unwind from a common cylindrical drum.
This maximum number of laminations is partly due to the fact that, as the spring assembly is moved along a straight line of transport, the sections of the individual laminations (or layers) begin to separate from each other. Moreover, as the number of laminations increase, the separation becomes more pronounced, requiring more and more space for the spring assembly to operate. This poses a substantial problem where space for a counterbalance system is limited. Such limits are imposed by size requirements for the robotic surgical system.
In addition, the conventional counterbalancing mechanisms have failed to provide a high degree of safety, reliability and mechanical redundancy, since such mechanisms do not sufficiently spread the tension force in the event of a failure by one of the laminations within the spring assembly. In other words, the presence of two or three laminations within the spring assembly does not provide an acceptable level of safety because the failure of one lamination would result in a substantial reduction of the counterbalance force (e.g., 33-50% of the counterbalanced weight). In addition, carrying higher loads in a spring lamination adversely reduces the useful life of the spring assembly so that it will not likely survive for the entire expected life of the robotic surgical system.